Bootstrap Current

A self-generated plasma current that reduces the external drive a machine needs.

A pressure gradient in a magnetised plasma spontaneously drives a component of the toroidal current — the bootstrap current. The more of the total current a plasma bootstraps, the less external current drive power it needs, improving the energy ledger.

HYPERION runs 9.66 MA of plasma current, of which the bootstrap fraction is 15.2%; the remainder is externally driven. Raising the bootstrap fraction is a standard efficiency lever.

The bootstrap current is a gift from neoclassical physics: a pressure gradient drives toroidal current for free, reducing the external drive a steady-state machine must supply. Raising the bootstrap fraction is a central efficiency goal, but it is bounded by stability. HYPERION bootstraps 15.5% of its 9.66 MA, with the remainder driven by neutral beams and radio-frequency systems.